1. The problem statement, all variables and given/known data I am trying to identify every force in this system and prove that it is in mechanical equilibrium when tan(θ)=⅓. Initially I had to solve it by finding when the derivative of potential with respect to θ was 0, but now I am just trying to resolve the forces. 2. Relevant equations Upwards forces = Downwards Forces Clockwise moments = Anticlockwise moments 3. The attempt at a solution First I let m=3 and g=9.8. I worked out the tension T in the string knowing that it must equal the weight of the particle, giving 29.4N. I worked out the forces on each of the pulleys assuming the tension on either side of them is equal. At A it will be 2Tcos(θ/2) which is 58.0 and at D it will be 2Tcos(1/2*(90-θ)) for which I got 47.7. Also you know that the force on E by the string will be equal to the tension so 29.4N. A quick check of these forces balancing horizontally shows that I am right. Now where I am stuck is on the vertical forces. I am not sure how the reaction forces at B and C and the reaction force between the two rods at A play a role and how could I work them out to show that they balance?